Production of a semiconductor device involves a step of forming an electroconductive film on a surface of a wafer to form a wiring layer by photolithography, etching or the like; a step of forming an interlaminar insulating film on the wiring layer; and the like; and an uneven surface made of an electroconductive material such as metal and an insulating material is formed on the surface of a wafer by these steps. In recent years, processing for fine wiring and multilayer wiring have been advancing for the purpose of higher integration of semiconductor integrated circuits, and accordingly techniques of planarizing an uneven surface of a wafer have become important.
As the method of planarizing an uneven surface of a wafer, a CMP method is generally used. CMP is a technique in which while the surface of a wafer to be polished is pressed against a polishing surface of a polishing pad, the surface of the wafer is polished with an abrasive in the form of slurry having abrasive grains dispersed therein (hereinafter, referred to as slurry).
As shown in FIG. 1, a polishing apparatus used generally in CMP is provided, for example, with a polishing plate 2 for supporting a polishing pad 1; a supporting stand (polishing head) 5 for supporting a subject to be polished (wafer) 4; a backing material for uniformly pressurizing a wafer; and a mechanism of feeding an abrasive. The polishing pad 1 is fitted with the polishing plate 2, for example, by sticking with a double-sided tape. The polishing plate 2 and the supporting stand 5 are provided with rotating shafts 6 and 7, respectively, and are arranged such that the polishing pad 1 and the subject to be polished 4, both of which are supported by them, are opposed to each other. The supporting stand 5 is provided with a pressurizing mechanism for pressing the subject to be polished 4 against the polishing pad 1.
When such CMP is conducted, there is a problem of judging the planarity of wafer surface. That is, the point in time when desired surface properties or planar state are reached is required to be detected. With respect to the thickness of an oxide film, polishing speed and the like, the following has been conventionally conducted that a test wafer is periodically treated, the results are confirmed, and thereafter a wafer to be a product is subjected to a polishing treatment.
In this method, however, the treatment time of a test wafer and the cost for the treatment are wasteful, and the test wafer not subjected to processing at all in advance and a product wafer are different in polishing results due to a loading effect unique to CMP, and accurate prediction of processing results is difficult without actual processing of the product wafer.
Accordingly, there has been a need in recent years for a method capable of in situ detection of the point in time when desired surface properties and thickness are attained at the time of CMP processing, in order to solve the problem described above. In such detection, various methods are used. From the viewpoints of measurement accuracy and spatial resolution in non-contract measurement, optical detection means comes to be used mainly.
The optical detection means is specifically a method of detecting the end-point of polishing by irradiating a wafer via a polishing pad through a window (light-transmitting region) with light beam, and monitoring interference signal generated by reflection of the light beam.
Patent Document 1 discloses a polishing body having a window, for example, a window consisting of two or more plates of transparent materials that are laminated, wherein the compressive elastic modulus of the transparent material that is positioned on the side of a subject to be polished is smaller than the compressive elastic modulus of the transparent material that is positioned on the opposite side from the subject to be polished.
In addition, Patent Document 2 discloses a polishing pad provided with a polishing layer and a translucent window member, wherein the outermost layer of the polishing surface side of at least the translucent window member is composed of a soft translucent layer having a micro rubber A hardness of 60 degrees or less.
Further, Patent Document 3 discloses a polishing pad provided with a polishing layer and a translucent window member, wherein the translucent window member is at least laminated by a soft translucent layer having a micro rubber A hardness of 60 degrees or less and a hard translucent layer having a micro rubber A hardness of 80 degrees or more, and the soft translucent layer is positioned in the outermost layer of the polishing surface side.
Moreover, Patent Document 4 discloses a polishing pad having a polishing region and a light-transmitting region, wherein the light-transmitting region is formed by laminating an ultra-soft layer positioned in a pad surface side and a soft layer positioned in a pad rear face side, and the Asker A hardness of the ultra-soft layer is 25 to 55 degrees, the Asker A hardness of the soft layer is 30 to 75 degrees, and the Asker A hardness of the soft layer is larger than that of the ultra-soft layer.
Since the polishing pads disclosed in Patent Documents 1 to 4 employ a soft material in the outermost layer of the window, the occurrence of scratches can be suppressed to some extent, but cannot be sufficiently suppressed.